Both high levels of polyamines and methylated bases have been shown to be affiliated with the onset of rapid cellular proliferation. S-Adenosylmethionine (SAM) serves as the propylamino donor in the synthesis of polyamines and as the methyl donor in virtually all transmethylation reactions. In addition, SAM has been shown to be a regulatory molecule in a variety of biological reactions. The overall objective of this research proposal is to determine the SAM-related biochemical and genetic mechanisms associated with the initiation of mitosis. An excellent opportunity for studying the molecular events necessary for the initiation of cell division is provided by the germination and outgrowth of yeast ascospores. We have found that the function of SAM during the cell cycle is to act as a stimulus of the Gl to S transition, to act as a precursor of polyamines which apparently regulate the rate of growth, and to act as a precursor of adenine, whose salvage from SAM is initiated during the cycle. The extracellular role of SAM in the Gl to S transition will be explored by studying the environmental conditions necessary for the SAM-stimulatory effect to be exerted, the necessity for macromolecule biosynthesis, the effect of SAM on transport systems, the specificity of the SAM molecule, and the mode of action of SAM, particularly at the level of the plasma membrane. The methods for the elucidation of the role of polyamines will utilize polyamine mutants and inhibitors of the SAM decarboxylase and ornithine decarboxylase. With polyamine-deficient spores, the effect of polyamine deficiency on cell division, macromolecule synthesis, uptake of nutrients and enzyme activities can be determined. The salvage of adenine from SAM should help clarify the relationship between purine salvage from SAM and the initiation of cell division. These studies should aid in our understanding of the biochemical and genetic mechanisms associated with rapidly proliferating tissues such as malignant neoplasms.